A turbo-charged internal combustion engine includes additional components and physical processes in both the intake and exhaust stream. On the intake side of the engine, a centrifugal compressor and intercooler are provided and are located between the air cleaner and a throttle valve. On the exhaust side, a turbine and a waste-gate—which defines a parallel exhaust stream path with the turbine—are both located between the exhaust manifold and the catalyst/muffler. It is known to provide an engine management system (EMS) configured to control the operation of a turbo-charged engine, including boost control. However, such an EMS is conventionally configured to perform its functions with only a minimal amount of additional information, notwithstanding the increased system complexity, in order to maintain reduced costs (i.e., by reducing the number of sensors). Conventionally, the additional sensors added when an engine is turbo-charged are all located on the intake side (e.g., a boost pressure sensor and boost temperature sensor).
As to boost control, conventional systems do not adequately address efficiency considerations. More specifically, conventional controls do not adequately address the desire for producing the optimum amount of boost for a needed amount of engine torque. As a result, the turbine presents an unnecessarily large restriction to the engine exhaust, which decreases efficiency. Also, the compressor ends up producing too much boost, which must thereafter be decreased downstream by the intake throttle, also resulting in operating inefficiency. This unnecessarily decreases fuel economy. Also, conventional control systems are specific to a particular implementation type, which reduces its applicability to other waste-gate mechanization approaches.
There is therefore a need for a system and method for controlling the boost pressure to a turbo-charged engine that minimizes or eliminates one or more of the problems set forth above.